In a medium bowl, stir together cream cheese and cheddar cheese. Stir in reserved bacon and, if you like, garlic. Spoon mixture into mushroom tops, and place them on a greased 15x10x1-inch baking pan.

Bake in a 350 degrees oven for 25 to 30 minutes or until mushrooms are tender. Let stand 5 minutes before serving.

Make Ahead Tip

Stuffed mushrooms taste best hot from the oven, but they're still a great make-ahead snack. Assemble the mushrooms up to 24 hours ahead of your party, then store them, covered, in the refrigerator until you're ready to bake them.